A long-standing goal of the golf ball design and manufacturing community is to select the various design parameters of a golf ball to optimally address its playability whilst satisfying all of the United States Golf Association (“USGA”) Rules of Golf. According to USGA regulations, the weight of a golf ball cannot exceed 1.620 ounces (avoirdupois), nor can the diameter of the ball be less then 1.680 inches. The USGA further stipulates that the initial velocity of the golf ball cannot exceed 255 feet per second and the driver distance must be less than 320 yards, both under controlled hitting conditions with a mechanical golfer. And finally, a golf ball must be spherically symmetric.
For many years, “the undisputed champion of performance golf balls featured rubber-windings wrapped around a liquid-filled core” (Johnson, “Mortally Wounded: Hot, New Solid-Core Balls Have Nearly KO'd Their Wound-Ball Rivals,” GolfDigest, June 2001). A superlative example of the three-piece, “liquid-center, thread-wound golf ball” is described in U.S. Pat. No. 5,597,365 to Yamada et al. Today, one is hard-pressed to find any so-called “wound” golf balls on the market. New materials and modernized manufacturing processes (in combination with certain market trends and other economic forces) have nearly forced the three-piece, wound golf ball into obsolescence.
With few exceptions, most golf balls fall into one of three different categories:
(1) Two-Piece, Solid-Core;
(2) Multi-Layer, Solid-Core; or
(3) Multi-Layer, Liquid-Core.
Category 1 balls (Two-Piece, Solid-Core) are typically constructed of a rubber-like polymeric core, surrounded by a thermoplastic ionomer cover. Examples of this ball include the Top-Flite XL (Top-Flite Golf Company, Carlsbad, Calif.) and the Titleist DT SoLo (Acushnet Company, Fairhaven, Mass.). Although these balls are easier to manufacture, due in-part to their economy of design, they are considered by some to have limited playing characteristics with regard to feel and spin.
Category 2 balls (Multi-Layer, Solid-Core) typically have one or more solid (i.e., “non-wound”) mantle layers juxtaposed between a solid inner core and outer cover. More often than not, the core material is made of polybutadiene, or a close relative, and the cover is constructed of a thermoplastic-ionomer inner cover and a castable urethane outer cover. Examples of this ball include the Srixon Z-URS (Sumitomo Rubber Industries, Ltd., Hyogo-ken, Japan) and the Nike One Platinum (Nike Inc., Beaverton, Oreg.).
Category 3 balls (Multi-Layer, Liquid-Core) are typically constructed of one or more solid (i.e., “non-wound”) mantle layers juxtaposed between a liquid core and outer cover. Examples of this construction are disclosed in U.S. Pat. No. 5,919,100 to Boehm et al. and U.S. Pat. No. 6,299,550 to Molitor et al. Arguably, some golf balls fall outside of these traditional categories. For example, U.S. Pat. No. 6,976,925 to Owens et al. describes a golf ball with a hollow-steel-core, surrounded by an intervening mantle layer and ionomer cover.
To date, golf ball designers and manufacturers have advanced the art of golf ball fabrication by ingenious construction geometry and a judicious selection of materials. However, there is a certain class of materials that have been largely overlooked by the golf ball design and manufacturing community. These so-called “smart” or “intelligent” materials exhibit a change in certain material properties as a function of some externally applied stimulus (see Rogers, “Intelligent Materials,” Scientific American, September 1995, pp. 154-157).
In what might be the first golf ball implementation of a smart material, U.S. Pat. No. 6,794,472 to Harris et al. describes the use of a “self-healing” polymer to autonomously improve the durability of a golf ball. In a method that was first reported by White et al., “Autonomic Healing of Polymer Composites” Nature 409:794-797 (2001), microencapsulated healing agents are released upon crack intrusion. U.S. Pat. No. 6,794,472 to Harris et al. contends that these healing agents will enable a golf ball to automatically mend micro-cracks that occur during play. Although this self-healing mechanism might increase the longevity of a golf ball, it does little to impact the ball's playability. In other words, a player's handicap is typically not influenced by the longevity of a golf ball.
Accordingly, there exists a need for a paradigm shift in the design and manufacture of golf balls that employ smart, nano-engineered materials to elevate the performance of play.